The invention relates to staplers, and more particularly, to staplers utilizing potential energy to assist in operating the staple drive mechanism. Potential energy or spring assisted office staplers have traditionally been of two types; either a stationary adaptation of powerful tacker-type models or a stationary stapler whose spring assist cannot achieve full power to drive and clinch the required sheet capacity without additional user applied force.
Typically, in a tacker-type stapler the staples are driven into the target object but the leg of staples are not bent. The strong force that is required for driving the staples is obtained by releasing the pressure that is accumulated in a spring or elastic member. Further, this structure that stores pressure in the spring can be of many different types but all are typically structured such that when the stapler is not in operation, the blade is located in front of the staples and when the blade is lifted, the staples move forward in the magazine. The blade is then lowered to drive one of the staples that has been pushed forward. This entire series of operations are executed in one instant with a powerful flow of force. Such a tacker is illustrated in U.S. Pat. No. 6,145,728. A stationary stapler adaptation of a similar mechanism is illustrated in U.S. Pat. No. 6,918,525.
In this type of tacker-type stapler configuration, when nothing is being stapled, there is a danger of staples flying out of the tacker inadvertently and it was necessary to develop a more complex structure in order to prevent such erroneous operations. Further, what is then seen in the tacker-type is a stationary configuration which requires loading the stapler from the rear due to the driver being in front of the staples and not lifted except during stapler operation. As a result, when the staples are reloaded, either the base or the magazine frame would have to be rotated and opened and the staples would then be fed. As such, more complex structures were adopted for each of inadvertent operation and staple reloading.
In the second type, spring assisted power has been applied within stationary staplers with a raised driver and without rear staple loading. However, previous approaches achieved very limited power gain given the limitations of known spring trigger mechanisms, known driver engagement mechanisms or other related linkages. These constructions only partly automate the function of the stapler and require additional manual force be applied to the driver when a stapler is operated at its sheet capacity, otherwise the staple would not be fully clinched under the paper. A stationary stapler adaptation of such an assist mechanism is illustrated in U.S. Pat. No. 5,356,063.
Both known types utilize locking mechanisms which act directly on the driver blade. These locking mechanisms intermittently experience functional problems including reduced power transmission to the driver, premature component failure, unreliable actuation and difficulty in returning to the rest position.